Palladium films act as excellent barrier layers for preventing migration of other metals in a substrate, such as an electrical contact, to the surface of the contact where oxidation of the other metal could take place. Palladium films are often made on a substrate by electroplating, vacuum sputtering, and laser direct-write metallization. Palladium is difficult to electroplate due to embrittlement on account of hydrogen induced cracking as the palladium is deposited. Palladium can also be deposited using electroless methods. Despite problems associated with electroplating and electroless methods, these processes are still used. Palladium films are best made by vacuum techniques such as chemical vapor deposition (CVD), metal-organic chemical vapor deposition (MOCVD), or sputtering.
In Gozum, et al. (Gozum, John E.; Pollina, Deborah M.; Jensen, James A.; Girolami, Gregory S. J. Am. Chem. Soc. 1988, 110, 2688), the chemical vapor deposition of a palladium layer is reported using bis(allyl)palladium, bis(2-methylallyl)palladium, and (cyclopentadienyl)(allyl)palladium as the starting precursor. The chemical vapor deposition of these precursors was accomplished at 250.degree. C. at 10.sup.-4 Torr. Palladium films were grown on substrates such as glass, steel, copper, and aluminum.
Gold can be deposited onto a substrate by decomposing a gold precursor. For example, in U.S. Pat. No. 4,933,204, a method is shown for depositing gold features on a substrate. Gold(III) hydroxide is dissolved in acetic acid to form gold(III) acetate. Gold features were then formed by casting the gold(III) acetate film on a suitable substrate such as silicon, and then traversing the film with a laser in the locations where it is desired to produce the conducting lines. The laser was operated at a power and speed sufficient to heat the traversed locations to a temperature above about 175.degree. C. The gold(III) acetate was decomposed under the heat from the laser to release a layer of gold on the surface of the substrate and release the acetate.
What is needed is a milder method for depositing a layer of palladium on a substrate. What is further needed is a method which does not require the use of a vacuum for deposition, electroplating or electroless methods.